I have the AirAid and got it mainly because it was the least expensive available. I have heard the K&N will make more power, but how much more is probably negligible. I really think it all comes down to personal taste. The other thing I liked about the AirAid was the fact it kept the stock tube and Nissan Logo, which covers the front of the engine and gives it a finished appearance. Again this is just my personal preference, others may not care about that aspect. Lastly, it is super simple to install and remove if needed! I'm sure others will be along to share their thoughts on the K&N, so hopefully you'll get the information you need to make an informed decision! Good luck, and keep us posted on what you decide!
I have an Airaid due to price and the way it looks.. keeping the stock Nissan cover. I leave it on when I go to the dealer along w/ my magnaflow exhaust and they never bother me. It all depends on which dealer you go to though. They made a mistake w/ parts so they owe me one big time due to several extra trips I had to make so if they ever hassle me about it I'll just bring that up 8)